Master student Projects

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Projects for Master students in the Nikhef B-physics (LHCb) group 2017 - 2018

date: April 2018

This is an overview with all available Master student projects in the Nikhef B-physics (LHCb) group.

If you have your own research proposal, need more detailed information on the (availability) of individual proposals or would like to discuss about other available projects in the group you are always welcome to contact either the contact person for the project and/or the Nikhef B-physics group leader:

Marcel Merk [e-mail:, Tel 020-5925107, Nikhef room N243]

For an overview of the theses written in the Nikhef B-physics group you can look at the Nikhef LHCb theses page

(The full list of projects at Nikhef can be found here.)

Master projects in the Nikhef B-physics group

1) Searches for new pentaquarks

Supervisor : P. Koppenburg (staff)

Research Description:

In 2015 LHCb surprisingly discovered states containing five quarks, called Pc+ pentaquarks. Such particles question our understanding of confinement, the principle that forces quarks to remain in a single hadron. Which hadrons are allowed and which are not? The pentaquarks were found in the decay of the Lambda_b baryon to a Pc+ and a kaon, and Pc+ to a J/psi and a proton. This project aims at studying other similar but yet unobserved decays which could reveal the presence of the know Pc+, or yet unknown pentaquarks. The student will optimise a selection for finding such a decay in LHCb data using machine learning techniques.

Relevant information:

[1] arXiv:1507.03414 (the pentaquark paper)

[2] arXiv:1406.0755 (a paper by P. Koppenburg similar to what the project could lead to).

2) Measurement of BR(B0 -> Ds+ Ds-)

Supervisors: Sevda Esen (postdoc), Niels Tuning (staf), Michele Veronesi (PhD)

Research description:

This project aims to discover the branching fraction of the decay B0->Ds- Ds+. The decay B0->Ds- Ds+ is quite rare, because it occurs through the exchange of a W-boson between the b and the d-quark of the B0-meson. This decay proceeds via Cabibbo-suppressed W-exchange and has not yet been observed; theoretical calculations predict a branching fraction at the order of 10^-5 with a best experimental upper limit of 3.6x10^-5.

A measurement of the decay rate of B0 -> Ds+Ds- relative to that of B0 -> D+D- can provide an estimate of the W-exchange contribution to the latter decay, a crucial piece of information for extracting the CKM angle gamma from B0 -> D(*)D(*).

The aim is to determine the relative branching fraction of B0->Ds+Ds- with respect to B0->Ds+D- decays (which has the best known branching ratio at present, (7.2 +- 0.8)x10^-3), in close collaboration with the PhD. The aim is that this project results in a journal publication on behalf of the LHCb collaboration. For this project computer skills are needed. The ROOT programme and C++ and/or Python macros are used. This is a project that is closely related to previous analyses in the group. Weekly video meetings with CERN coordinate the efforts with in the LHCb collaboration.

Relevant information:

[1] M.Jung and S.Schacht, "Standard Model Predictions and New Physics Sensitivity in B -> DD Decays"

[2] L.Bel, Bruyn, R. Fleischer, M.Mulder, N.Tuning, "Anatomy of B -> DD Decays"

[3] A.Zupanc et al [Belle Collaboration] "Improved measurement of B0 -> DsD+ and search for B0 -> Ds+Ds at Belle"

[4] B.Aubert et al. [Babar Collaboration] "Search for the W-exchange decays B0 -> DD+"

[5] R.Aaij et al. [LHCb Collaboration], "First observations of B0s -> D+D, Ds+D and D0D0 decays"

3) Measurement of relative ratio of B+ -> D0D+ and B+ -> D0Ds decays

Supervisors: Sevda Esen (postdoc), Niels Tuning (staf), Michele Veronesi (PhD)

Research description:

This decay is closely related to B0->Ds- Ds+ (see above), and close collaboration between the two master projects is foreseen. The decay mode B+->D0D+ is expected to be dominated by tree diagrams with some additional contributions from penguin diagrams. Assuming SU(3) symmetry, measurement of its branching fraction relative to Cabibbo-favored B+->D0D will enable better understanding of penguin contributions to the CP violating mixing phase.

Relevant information:

[1] L.Bel, Bruyn, R. Fleischer, M.Mulder, N.Tuning, "Anatomy of B -> DD Decays"

[2] R.Aaij et al. [LHCb Collaboration], "First observations of B0s -> D+D, Ds+D and D0D0 decays"

[3] PDG:

4) A search for heavy neutrinos in the decay of W at LHCb

Supervisors: Wouter Hulsbergen (staff), Elena Dall'Occo (PhD)

Research description:

Neutrinos are arguably the most mysterious of all known fundamental fermions as they are both much lighter than all others and only weakly interacting. It is thought that the tiny mass of neutrinos can be explained by their mixing with so-far unknown, much heavier, neutrino-like particles. In this research proposal we look for these new neutrinos in the decay of the SM W-boson using data with the LHCb experiment at CERN. The W boson is assumed to decay to a heavy neutrino and a muon. The heavy neutrino subsequently decays to a muon and a pair of quarks. Both like-sign and opposite-sign muon pairs will be studied. The result of the analysis will either be a limit on the production of the new neutrinos or the discovery of something entirely new.

5) A Scintillator Fibers Tracker

Supervisors: Antonio Pellegrino

Research description:

The LHCb collaboration is upgrading the present tracking system constructing a new tracker based on scintillating fibers combined with silicon photo-multipliers (SiPM): the SciFi Tracker! Nikhef plays a key role in the project, as we will build the SciFi fibers modules, the cold-box enclosure housing the SiPMs, and a large part of the on-detector electronics. In all these areas, interesting test hardware and software has to be realized, and several research topics for a Master project are available, taking the student in contact with state-of-the-art particle detectors, in a large team of physicists and engineers. Possible collaborations with the Nikhef R&D group can also be envisaged.

6) The Z forward backward asymmetry

Supervisors: Wouter Hulsbergen

Research description:

The forward backward asymmetry of Z->mumu decays probes the standard model weak mixing angle, providing a strong test of the standard model. A dominating systematic uncertainty in this measurement is the affect of detector misalignments. In this project Z->mumu events are used to improve the detector alignment and thereby increase the precision of the run-2 measurements.

7) Construction of the velo upgrade detector

Supervisors: Wouter Hulsbergen

Research description:

Nikhef contributes to the upgraded LHCb detector (installation 2019-2020) with the construction of vertex detector modules. In this project the student participates in the construction at Nikhef, in particular in R&D studies to determine the optimize the ‘gluing’ process (early 2018), and the analysis of the first test data taken with built modules (spring/summer 2018).

8) *Probing the dark sector with Y(1S)->4mu events*

Supervisors: Wouter Hulsbergen

Research description:

In certain parts of their parameter space Hidden Valley theories predict upsilon decays to two new dark sector particles that subsequently decay into two muons. These particles may or may not be long-lived. In this project we search for such events in LHCb run-2 data using the Turbo stream.

9) Measurement of the relative efficiency of muons and electrons with J/psi->ll decays

Supervisors: Patrick Koppenburg

Research description:

LHCb has produced intriguing results hinting at violation of lepton universality. As extraordinary claims require extraordinary evidence we propose to perform a measurement of the relative reconstruction efficiency of electrons and muons by comparing the number of J/psi particles counted in the di-electron and di-muon final states.

10) Very rare decays of B mesons

Supervisors: Marcel Merk

Research description: Decays of B-mesons to a pair of muons or a pair of electrons are very strongly suppressed in the Standard Model. As a consequence these decays are sensitive to virtual contributions of particles beyond the Standard Model. The project includes a theoretical study on these sensitivties and/or experimental improvements to the measurement.

11) Measurement of Central Exclusive Production Rates of Chi_c using converted photons in LHCb.

Supervisor: Kazu Akiba

Research description: Central exclusive production (CEP) of particles at the LHC is characterised by a extremely clean signature. Differently from the typical inelastic collisions where many particles are created resulting in a so-called Primary Vertex, CEP events have only the final state particles of interest. In this project the particle of interest is a pair of charmed quarks creating a chi_c particle. In theory this process is generated by a long range gluon exchange and can elucidate the nature of the strong force, described by the quantum chromodynamics in the the standard model. The proposed work involves analysing a pre-existing dataset with reconstructed chi_c and simulating events at the LHCb in order to obtain the relative occurrence rate of each chi_c species (spins 0, 1, 2), a quantity that can be easily compared to theoretical predictions.

12) Optimization studies for Vertex detector at the High Lumi LHCb

Supervisor: Kazu Akiba

Research description: The LHCb experiment is dedicated to measure tiny differences between matter and antimatter through the precise study of rare processes involving b or c quarks. The LHCb detector will undergo a major modification in order to dramatically increase the luminosity and be able to measure indirect effects of physics beyond the standard model. In this environment, over 42 simultaneous collisions are expected to happen at a time interval of 200 ps where the two proton bunches overlap. The particles of interest have a relatively long lifetime and therefore the best way to distinguish them from the background collisions is through the precise reconstruction of displaced vertices and pointing directions. The new detector considers using extremely recent or even future technologies to measure space (with resolutions below 10 um) and time (100 ps or better) to efficiently reconstruct the events of interest for physics. The project involves changing completely the LHCb Vertex Locator (VELO) design in simulation and determine what can be the best performance for the upgraded detector, considering different spatial and temporal resolutions.

13) Measurement of charge multiplication in heavily irradiated sensors

Supervisor: Kazu Akiba

Research description: During the R&D phase for the LHCb VELO Upgrade detector a few sensor prototypes were irradiated to the extreme fluence expected to be achieved during the detector lifetime. These samples were tested using high energy particles at the SPS facility at CERN with their trajectories reconstructed by the Timepix3 telescope. A preliminary analysis revealed that at the highest irradiation levels the amount of signal observed is higher than expected, and even larger than the signal obtained at lower doses. At the Device Under Test (DUT) position inside the telescope, the spatial resolution attained by this system is below 2 um. This means that a detailed analysis can be performed in order to study where and how this signal amplification happens within the 55x55 um^2 pixel cell. This project involves analysing the telescope and DUT data to investigate the charge multiplication mechanism at the microscopic level.

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